The plan, which has received some encouragement from Gov. Jerry Brown’s top bullet train appointee, represents a major shift in thinking about the first phase of the nearly $100-billion project.

Until recently, the project was expected to draw down only about one-third of its $9-billion bond fund in coming years to help pay for a 130-mile rail segment in the Central Valley. The new proposals call for spending an additional $4 billion upfront on improvements that could speed up existing passenger service in two of the state’s biggest metropolitan areas and prepare for the eventual arrival of bullet trains.

Proponents say the strategy would ensure near-term benefits from the state’s high-speed rail outlays even if development of the full system stalls.

“We ought to be investing whatever is available now to show California and the rest of the country the benefits of high-speed rail very soon,” said Jose Luis Moscovich, executive director of the San Francisco County Transportation Authority. “We believe there can be simultaneous efforts in Southern California and on the peninsula” between San Francisco and San Jose.